1. Field of the Invention
This invention relates to a method of eliminating interference signals from video signals by means of motion-adaptive filtering.
2. Description of the Related Art
For the purpose of eliminating interference signals, recursive filtering, transversal filtering and median filtering are generally used in video technology. The recursive and transversal filtering methods are satisfactory as linear filtering methods for reducing equally distributed (white) noise, while the non-linear median filtering method has advantages in the elimination of impulsive noise. In practice, recursive filtering is often preferred to transversal filtering due to the smaller number of components required and the higher noise reduction, although a linear phase and a constant group delay time are obtained with the transversal filtering method. Circuit structures for linear filters for eliminating interference signals are well known. To characterize median filters, the associated filter window will be described. This window indicates the number and location of samples of a function to be filtered. When (digital) video signals are used, the filtering operation can be performed in all three dimensions (horizontal, vertical and temporally). Such median filters are described in DE-A-40 01 552, corresponding to U.S. Pat. No. 5,148,278. A drawback of this implementation is that the filter window is constant. For example, upon motion, artefacts in the form of loss of sharpness and aliasing may occur.